You must then add the image to each slider as follows:
1. Select Weblizer Slider> Add New Slide.
2. Click Slider Image under Slider Background Image.
4. Select Media Library in pop-up.
5. Select Show next to slider_background.
6. Click Attachment Post URL in pop-up.
7. Click Insert into Post.
8. Enter the other information for the slider then Publish. Repeat this process for each slide.

As far as I can tell, this means that you can only use one background image.